Submarine cable-burying devices

ABSTRACT

A plow-type cable-burying device for use in placing communication and power transmission cables under ground under a body of water has a protective blade, cultivating blades and a plow-type digging blade arranged in succession in the order as mentioned along a tubular body for guiding a cable to be buried in the ground under water. The tubular body is stabilized by sledges and the cable is further guided by a plurality of cable guide cylinders.

United States Patent Shiroyama et al.

[ July 23, 1974 SUBMARINE CABLE-BURYING DEVICES inventors: Kaisuke Shiroyama, Yokohama;

Takeo Yokoyama, Kamakura, both of Japan The Furukawa Company Limited, Tokyo, Japan Filed: June 7, 1972 Appl. No.: 260,430

Assignee:

Foreign Application Priority Data Nov, 15, 1971 Japan 46-90661 Nov. 15, 1971 Japan 46-90662 May 8, 1972 Japan 47-53340 US. Cl. 6l/72.4, 6l/72.6 Int. Cl E021 5/02, F161 1/00 Field of Search 61/724, 72.1, 72.6, 72.7,

References Cited UNITED STATES PATENTS Lilly 61/72.?

2,067,717 1/1937 Lawton et al 61/724 2,144,063 1/1939 Irvin 61/724 2,602,300 7/1952 Collins l A A l r 61/724 2,647,758 8/1953 Ryan 37/193 X 2,992,537 7/1961 Callahan... 61/724 3,333,432 8/1967 Hale et a1. 61/724 Primary Examiner-Jacob Shapiro [57] ABSTRACT A plow-type cable-burying device for use in placing communication and power transmission cables under ground under a body of water has a protective blade, cultivating blades and a plow-type digging blade arranged in succession in the order as mentioned along a tubular body for guiding a cable to be buried in the ground under water. The tubular body is stabilized by sledges and the cable is further guided by a plurality of cable guide cylinders.

8 Claims, 9 Drawing Figures PAINTED-"1231914 SKHBNG QQ mm km W\ k AQK PAIENIEBJHLM 3.824.798

SHEET 6 0f 6 FIG. .9

1 SUBMARINE CABLE-BURYING DEVICES This invention relates to submarine cable-burying devices for laying communication and power transmission cables under ground under a body of water, and more particularly to a plow-type cable-burying device.

A submarine cable placed on the ground under water is liable to be damaged by underwater objects towed or dragged across the cable such as fishing trawler equipment or anchors or to such abuse as abrassive wear caused by friction with the ground under water. Thus, it is necessary to bury the cable in the ground under water.

l-leretofore, it has been proposed to lay the cable on the ground under water and then dig a trench for burying the cable therein along the cable by means of jetting nozzles that direct streams of water or plow-type digging blades.

Such cable burying operation comprising two steps of laying the cable on the ground under water and then digging the trench for burying the cable therein, which is usually influenced by the weather and sea conditions so that the cable burying operation period is extended and the operating costs become expensive. Moreover, the cable-burying device is dragged by a ship to dig the trench along the cable, but it is difficult to operate the cable-burying device on the ground under water from the ship such that the cable-burying device moves along the cable placed on the ground under water. Thus, the cable burying operation must be carried out by taking the greatest care, thereby lowering the operating efficiency. The cable-burying device provided with plowtype digging blades is simple in construction when compared with that provided with the jetting nozzles that direct streams of water. But, the conventional plow-type cable-burying device consisting of a plateshaped body provided with the plow-type digging blades has the disadvantage that the plow-type cableburying devices must be dragged by a large dragging forces, that the trench digging operation is not efficient, that the cable could not be extended from the towing ship to the cable-bu rying device without dipping it downwards, and that the cable delivered from the towing ship could not be simultaneously laid and buried in the ground under water.

An object of the invention, therefore, is to provide an improved plow-type cable-burying device which can be dragged by a relatively small towing force.

Another object of the invention is to provide such an improved plow-type cable-burying device which is efiicient in the trench digging operation.

Yet another object is to provide such an improved plow-type cable-burying device which can extend the cable from the towing ship to the cable-burying device without giving appreciably large downwards dipping, and which may be constructed on a relatively cheap and economical basis.

A still further object of the invention is to provide such an improved plow-type cable-burying device which is capable of simultaneously effecting a relatively high speed cable laying and burying operations at a relatively low power consumption level.

Other objects will appear in the following specification, reference being made to the drawings, in which:

FIG. 1 is a diagrammatic illustration of a cableburying operation utilizing a plow-type cable-burying device according to the invention;

FIG. 2 is a plan view of a first embodiment of a plowtype cable-burying device according to the invention;

FIG. 3 is its side elevation;

FIG. 4 is a sectional view taken along the line IVIV of FIG. 3;

FIG. 5 is a sectional view taken along the line V-V of FIG. 3;

FIG. 6 shows similarly to FIG. 4 a sectional view of a second embodiment of a plow-type cable-burying device according to the invention;

FIG. 7 is a side elevation of a third embodiment of a plow-type cable-burying device according to the invention, in which a part is broken away to show a digging blade driving mechanism;

FIG. 8 is a sectional side elevation of a fourth embodiment of a plow-type cable-burying device accord ing to the invention; and

FIG. 9 shows similarly to FIG. 8 a side elevation for assisting in the description of the plow-type cableburying device shown in FIG. 8.

Referring first to FIG. I, there is diagrammatically shown a plow-type cable-burying device 1 according to the invention which is dragged by a ship 2 on the surface of the water by means of towing wires 3. A cable 4 to be buried in the ground under water is delivered from the towing ship 2 through a brake device 5 and introduced in a trench 6 dug by the cable-burying device 1. The brake device 5 serves to absorb the dipping tension of the cable 4 caused by its own weight.

Now, the plow-type cable-burying device 1 will be described in detail with reference to FIGS. 2 to 5.

The cable-burying device I shown in FIGS. 2 to 5 comprises a tubular body 1] made of steel and having at its rear end a downward bent portion Ila adapted to guide the cable 4 into the trench 6 (FIG. I) dug by the device 1 in the ground under water. The tubular body 11 is provided with brackets I2, 12, one on each side thereof and to the downwards extending free end of which is secured a sledge 13. The sledges 13, 13 are adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of the tubular body 11. Thus, the stabilizing sledges 13, 13 are capable of preventing the cable-burying device I from being upset, and as a result, the device 1 can reliably dig the trench 6 in a stable manner.

The tubular body 11 is provided at its rear lower portion with a plow-type digging blade 14, a protective blade 15 and at least two (four in the present embodiments) cultivating blades l6, 16', two on each side of the protective blade 15 in the front of the digging blade 14. The plow-type digging blade 14 is secured to the rear portion of the tubular body 11 and consists of a digging portion having at its front end a sharp knife edge and a hollow soil expelling portion 14b whose width is equal to or a slightiy wider than the outer diameter of the tubular body II and having concave end edges. The plow-type digging blade 14 is adapted to dig the ground under water to form the trench 6 in which is placed the cable 4. The protective blade 15 is relatively thin and has at its front edge a sharp knife edge and located at the center of the tubular body 11 and extends upwards from the lower edge of the digging blade 14 along the lower edges of the cultivating blades 16, 16 to the lower portion of the tubular body 11. The protective blade 15 is adapted to be brought into contact with the ground under water prior to the cultivating blades 16, 16' and digging blade 14 and hence prevents the cultivating blades 16, 16' and the digging blade 14 from biting into the rock or rock bed. The front cultivating blades 16' are smaller in height than the rear cultivating blades 16 and the cultivating blades 16, 16' as a whole serve to loosen the sand of the ground under water prior to the formation of the trench 6 by the digging blade 14, thereby facilitating the digging operation of the digging blade 14.

The tubular body 11 is provided at its front end with a metal fitting 17 to which two towing wires 3, 3 are detachably connected for dragging the device 1 from the ship 2. These towing wires 3, 3 are connected through the metal fittings 17 to the tubular body 11 and extend through a plurality of cable guide cylinders 18. Each cable guide cylinder 18 consists of two halves 19, 19' having flanges 20, 20', respectively, and held together by bolts 21 passing through bores formed in these flanges 20, 20'. The towing wires 3, 3 extend through holes 22, 22 formed between the flanges 20, 20'. The cable guide cylinders 18 serve to prevent the towing wires 3, 3 from being dipped downwards by their own weight and hence prevent the front end of the cableburying device 1 from being raised upwards, and as a result, the digging depth is prevented from becoming decreased. The cable guide cylinders 18 may be separted one from the other and each cable guide cylinder may provide at its side with at least one wire guide (not shown) through which is extended at least one towing wire 3. In this case, the cable guide cylinders 18 are loosely supported by the towing wire 3.

When the cable-burying device 1 constructed as above described according to the invention is dragged by the towing wires 3, 3 and proceeds on the ground under water in a given direction, the device 1 is dept in its stable attitude by means of the stabilizing sledges 13, 13 adapted to remain in contact with the ground under water in spite of variations in the ground contour. The protective blade 15, cultivating blades 16, 16 and plow-type digging blade 14 are brought into contact with the ground under water in the order as mentioned to dig the trench 6 and at the same time the cable 4 is introduced to the trench 6 through the tubular body 11 without undully dipping the cable 4 owing to the presence of the cable guide cylinders 18.

As stated hereinbefore, a combination of the improved plow-type digging blades 14, l5, 16, 16', stabilizing sledges l3, l3 and cable guide cylinders 18, according to the invention makes it possible to improve the efficiency of simultaneously laying and burying the cable 4 in the ground under water.

It is not always necessary to make the tubular body 11 circular in section. A suitable cable guide may also be connected to the rear end of the tubular body 11 for the purpose of introducing the cable 4 to the trench 6 in an easy manner. In the actual cable burying operation, the degree of span of the towing wires 3, 3, their lengths and the number of the cable guide cylinders 18 may suitably be selected.

If the ground is hard it is impossible to dig the trench. Particularly, if the cable-burying device 1 collides with the hard rock bed, etc. a large tension is given to the towing wires 3, 3, and as a result, there is risk of the towing wires 3, 3 being broken or of the towing ship 2 being stopped.

In order to avoid such troubles, the cable-burying device 1 must be removed from the cable 4 when the device l collides with the hard rock bed, etc. Moreover, when cable 4 is to be laid across a large body of deep water, for example, an ocean, it is necessary that the cable 4 be directly laid on the ocean bed without digging the trench 6.

The conventional cable-burying device has the disadvantage that even in such case the device must be removed from the cable in order to dig the trench 6. In the embodiment shown in FIG. 6, provision is made of two horizontal base plates 23, 23 secured one on each side of the tubular body 11. The brackets 12, 12 are vertically mounted on the base plates 23, 23 respectively, and made as supporting poles. The supporting poles 12, 12 are provided at their sides with jack mechanisms 24, 24, respectively, each consisting of a pneumatic cylinder. Each cylinder 24 extends vertically through the base plate 23 and provided at its upper end with a plunger 25 movably mounted therein and secured to the supporting pole l2 and provided at its lower end with the stabilizing sledge 13 secured thereto. Alternatively, each cylinder 24 may be secured to the supporting pole l2 and the lower end of the plunger 25 may be secured to the stabilizing sledge 13. Each cylinder 24 is provided at its upper side with a fluid opening 26 and at its lower side with a fluid opening 27. The fluid is supplied under pressure through these openings 26, 26 into the cylinders 24, 24 and exhausted through these openings 27, 27 out of the cylinders 24, 24, respectively.

The supporting poles 12, 12 are also provided with locking mechanisms 28, 28 each consisting of a cylinder 28 secured to the supporting pole l2 and a plunger 29 movably mounted in the cylinder 28. When the gas pressure is not supplied to the locking cylinder 28, the plunger 29 is urged against one of indentations 30 formed along the opposite side of the cylinder 24 by the action of spring (not shown) enclosed in the cylinder 28 to lock the supporting poles 12, 12 and hence the cable-burying device 1 at the desired depth H as showng in FIG. 6. The base plate 23 is provided at its top surface with gas reservoirs 31, 31 adapted to supply gas such as air or nitrogen gas under pressure to the jack mechanisms 24, 24 and to the lock mechanisms 28, 28 in response to the instruction received from the towing ship 2.

lf it is desired to lay and bury the cable 4 in shallow water in a constant depth, the supporting poles 12, 12 are immovably locked to the cylinders 24, 24 at the position shown in FIG. 6 by urging the plungers 29, 29 against one of the indentations 30, 30 by the springs (not shown) enclosed in the locking cylinders 28, 28. The use of the spring action of the springs enclosed in the locking cylinders 28, 28 is more superior to the use of the gas pressure of the jack mechanisms 24, 24 in case of laying long transoceanic cables.

Thus, the plow-type cable-burying device 1 is held at a desired depth and dragged to bite into the ocean bed. ln this case, the attitude of the device 1 and the digging depth are made constant with the aid of the stabilizing sledges 13, 13.

The digging depth is determined by the distance H which is parallel with that portion of the device 1 which extends from the lower surface of the stabilizing sledges 13, 13 to the lower end of the plow-type digging blade 14. The invention is capable of easily setting this digging depth by changing the locking positions of the device I. If the device 1 collides with the underwater objects such as the rock bed, etc. the signal is supplied from the towing ship 2 to supply gas under pressure into the locking mechanisms 28, 28 so as to retreat their plungers 29, 29 from the indentations 30, 30. Thus, the supporting poles 12, 12 are released and then the jack mechanisms 24, 24 are operated to extend the plungers 25, 25 to raise the device 1 through the supporting poles 12, 12 and the base plate 23, 23. Since the stabilizing sledges 13, 13 remain in contact with the ground under water in spite of variations in said ground contour, the lifting operation of the device 1 can reliably be effected in an easy manner. if the plow-type digging blade 14 is raised, the distance H from the lower surfaces of the stabilizing sledges l3, 13 to the lower end of the plow-type digging blade 14 becomes decreased, and as a result, the plow-type digging blade 14 can easily ride over the objects under water. After riding over the objects under water, the jack mechanisms 24, 24 are operated to lower the device 1 to the original condition and lock it. Then, the trench 6 is dug again to bury the cable 4 therein. When cable 4 is to be laid across a large body of deep water, for example, an ocean, it is not necessary that the cable 4 be buried in the ground under water. in such a case, the jack mechanisms 24, 24 are operated to lift the device 1 which may then be served to guide and lay the cable 4. In this case, the weight of the device 1 permits the cable 4 to be laid along a predetermined route, thereby preventing undersirable displacement of the cable 4 out of the predetermined route caused by underwater currents.

As explained hereinbefore, the provision of the jack mechanism 24, 24 for raising and lowering the device 1 makes it possible to lay the cable 4 even when the objects are present under water. Moreover, in case of simultaneously laying and burying the cable 4, if it is not required to dig the trench 6 the device 1 may be used as a cable guide without removing it from the cable 4.

In the embodiment of the cable-burying device shown in FIG. 7, the digging element 14a of the plowtype digging blade 14 is separated from the hollow soil expelling element 14b and pivotally mounted by means of a pivot pin 32 on a center plate 33 secured to the lower side of the tubular body 11.

The hollow soil expelling element 14b encloses therein a link mechanism 34 for swinging the digging element 140 about the pivot pin 32. The link mechanism 34 is connected at its one end to a crank mechanism 35 driven by a motor (not shown) and at its other end to a toggle link mechanism 36 whose front end is extended through a guide member 37 and pivotally supported by a pivot pin 38 secured to the digging element 14a.

In the plow-type cable-burying device as described above, if the motor (not shown) is energized from the towing ship 2 through a conductor (not shown) to rotate the crank mechanism 35 in a direction shown by an arrow, the digging element 14a is caused to swing about the pivot pin 32.

Thus, during the cable burying operation the digging element 140 is reciprocally swung to and fro as shown by arrows, and as a result, the trench digging operation can reliably be performed with a relatively small dragging force.

The conventional plow-type cable-burying device is required to drag the towing wires 3 by a dragging force of 12 tons at a speed of 1.5 knots of the towing ship in order to dig a trench 6 whose depth is l m in the fine sand bed under water, while the plow-type cable burying device 1 according to the invention as shown in FIG. 7 is capable of digging the same depth of trench by a dragging force of about 9 tons at a speed of 1.5 knots of the towing ship 2 under the conditions that the motor is rotated at 300 rpm. and the digging element is made to swing reciprocally with an amplitude of 5 cm.

As explained hereinbefore, the use of the digging element 14a adapted to swing to and fro with the aid of the link mechanism 34 ensures a reliable digging of the trench 6 by a relatively small dragging force and further provides the important advantage that the cable burying operation can reliably be performed by a relatively small ship 2, and as a result, the cable-burying costs become less expensive.

in the embodiment shown in F IG. 8, a weight 39 having a suitable value is mounted in a cavity 40 of the hollow soil expelling element 14b of the plow-type digging blade 14. The weight 4 is made of a metal having a relatively large specific weight, for example, lead. The weight 39 may be incorporated into cavity 40 by means of casting, pressing, etc. and made integral with the tubular body 11, filling up a part or whole of the cavity 40.

The reason why the attitude of the cable-burying device l is stabilized owing to the presence of the weight 39 will be described.

As seen from FIG. 9, the moment M applied to the cable-burying device 1 is given by M 1 Tsina 3 WSin0 1 30059 (lgRsinag 1 1 51119 l N sin0 where P is a center of rotation at that portion in the front of the stabilizing sledges 13 which is in contact with the ground under water, T is the dragging tension of the cable-burying device 1, W is the weight of the ca ble-burying device 1, F is the frictional force between the cable-burying device 1 and the ground under water, S is the vertical component of the digging force, R is the horizontal component of the digging force, N,, N, are the reactions of the gravity and of the vertical component of the digging force S, respectively.

In the above equation, if M=0, then the attitude of the cable-burying device 1 is in its stable condition. The attitude of the cable-burying device 1 is also in its stable condition if M Z 0 when R becomes larger.

Conversely, if M 0 when R becomes larger, then the rear portion of the cable-burying device 1 becomes raised, and as a result, the relative angle of the digging blade 14 is changed to decrease the vertical component of the digging force S, thereby making the digging operation unstable.

It might be expected to make the attitude of the cable-burying device 1 more or less stable by giving a large value to B, in the tenn of l Tsinfl, in the above equation. But, such results could not be obtained owing to the constructional point of view of the cable-burying device 1. Thus, it is necessary that 1;,Wsin 6 or I ScosO- be large for the purpose of stabilizing the attitude of the cable-burying device 1.

The cable-burying device 1 comprising the digging blade 14 projected from its lower portion and enclosing the weight 39 in the cavity 40 makes it possible to displace the center of gravity of the cable-burying device 1 as rear as possible, and as a result the term l Wsin becomes increased without increasing the weight of the cable-burying device 1 as a whole. Thus, the cableburying device 1 is capable of digging the ground under water to form the trench 6 without significantly increasing the weight of the cable-burying device 1 as a whole.

Tests were made by the use of 2.6-tons, 5 m-long plow-type burying device having no weight 39 in the digging blade and instead having a weight 39/ton on the arm, designed to dig a trench 6 in the depth of l m. The result was that the rear portion of the cable-burying device l rose 20 25 cm upwards, the digging depth being only 75 80 cm. The tension required for the digging operation was on the order of 10 tons and the dragging angle 30 40,while the same plow-type cable-burying device comprising the digging blade 14 with the weight 39 made of lead of 1 ton cast in the cavity 40 causes the total weight of the cable-burying device 1 to increase to 3.6 tons, but the tension required for the digging operation is not substantially changed and the attitude of the cable-burying device 1 becomes stable and can dig the trench 6 of predetermined depth of l m.

As explained hereinbefore, the plow-type cableburying device 1 comprising a tubular body 11 having at its rear portion a downwards bent portion 110, a plow-type digging blade 14 projecting from the lower portion of the tubular body 11 and a weight 39 incorporated in the cavity 40 of the digging blade 14 is relatively small in size and light in weight and is simple, easy and economical to transport and construct, and a trench 6 having a given depth can be dug with a stable attitude.

It is obvious to those skilled in the art that numerous changes and modifications may be made to the embodiments as they have been disclosed above without departing from the spirit and scope of the invention.

What is claimed is:

l. A plow-type cable-burying device comprising a tubular body consisting of a cable inlet portion extending in a direction in parallel with the ground under water, an intermediate bent portion gradually bent downward, and a cable outlet portion opened at the bottom of a trench being dug by the device, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade secured to said intermediate bent portion of said tubular body and provided in the front end thereof with a sharp knife edge and having side surfaces gradually diverging towards the rear portion thereof, and a plurality of cable guide cylinders each having at least one wire guide secured thereto and through which is extended said towing wire, said cable guide cylinders being supported by said towing wire.

2. A plow-type cable-burying device as claimed in claim 1 and further comprising a protective blade attached to said tubular body and extending along the lower side of its center line and adapted to be brought into contact with the ground under water prior to said cultivating blades and digging blade, thereby preventing said cultivating blades and digging blade from biting into the rock bed.

3. A plow-type cable-burying device comprising a tubular body through which is passed a cable to be buried in the ground under water, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade provided in the front end thereof with a sharp knife edge and attached to said tubular body in the rear of said cultivating blade and having side surfaces gradually diverging, towards the rear portion thereof, and a plurality of cable guide cylinders each consisting of two cylinder halves each having flange,

and held together by bolts passing through said flanges with said towing wires sandwiched therebetween and arranged side by side in the front of said tubular body to form an extension of said tubular body.

4. A plow-type cable-burying device comprising a tubular body through which is passed a cable to be buried in the ground under water, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade provided in the front end thereof with a sharp knife edge and attached to said tubular body in the rear of said cultivating blade and having side surfaces gradually diverging towards the rear portion thereof, said vertically mounted plow-type digging blade consisting of a hollow soil repelling element and a digging element swingably mounted in the front of said hollow soil repelling element. said hollow soil repelling element including a swing mechanism for swinging to and fro said digging element in the moving direction thereof.

5. A plow-type cable-burying device as claimed in claim 4 wherein said hollow soil repelling element is provided with a weight incorporated therein.

6. A plow-type cable burying device comprising a tubular body consisting of a cable inlet portion extending in a direction in parallel with the ground under water, an intermediate bent portion gradually bent downward, and a cable outlet portion opened at the bottom of a trench being dug by the device, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade secured to said intermediate bent portion of said tubular body and provided in the front end thereof with a sharp knife edge and having side surfaces gradually diverging towards the rear portion thereof, a plurality of cable guide cylinders each consisting of two cylinder halves each having flanges, and held together by bolts passing through said flanges with said towing wires sandwiched therebetween and arranged side by side in the front of said tubular body to form an extension of said tubular body.

7. A plow-type cable-burying device comprising a tubular body consisting of a cable inlet portion extending in a direction in parallel with the ground under water, an intermediate bent portion gradually bent downward, and a cable outlet portion opened at the bottom of a trench being dug by the device, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade secured to said intermediate bent portion of said tubular body and provided in the front end thereof with a sharp knife edge and having side surfaces gradually diverging towards the rear portion thereof, said vertically mounted plow-type digging blade consisting of a hollow soil repelling element and a digging element swingably mounted in the front of said hollow soil repelling element, said hollow soil repelling element including a swing mechanism for swinging to and fro said digging element in the moving direction thereof.

8. A plow-type cable-burying device as claimed in claim 7 wherein said hollow soil repelling element is provided with a weight incorporated therein.

l k f 

1. A plow-type cable-burying device comprising a tubular body consisting of a cable inlet portion extending in a direction in parallel with the ground under water, an intermediate bent portion gradually bent downward, and a cable outlet portion opened at the bottom of a trench being dug by the device, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade secured to said intermediate bent portion of said tubular body and provided in the front end thereof with a sharp knife edge and having side surfaces gradually diverging towards the rear portion thereof, and a plurality of cable guide cylinders each having at least one wire guide secured thereto and through which is extended said towing wire, said cable guide cylinders being supported by said towing wire.
 2. A plow-type cable-burying device as claimed in claim 1 and further comprising a protective blade attached to said tubular body and extending along the lower side of its center line and adapted to be brought into contact with the ground under water prior to said cultivating blades and digging blade, thereby preventing said cultivating blades and digging blade from biting into the rock bed.
 3. A plow-type cable-burying device comprising a tubular body through which is passed a cable to be buried in the ground under water, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade provided in the front end thereof with a sharp knife edge and attached to said tubular body in the rear of said cultivating blade and having side surfaces gradually diverging, towards the rear portion thereof, and a plurality of cable guide cylinders each consisting of two cylinder halves each having flange, and held together by bolts passing through said flanges with said towing wires sandwiched therebetween and arranged side by side in the front of said tubular body to form an extension of said tubular body.
 4. A plow-type cable-burying device comprising a tubular body through which is passed a cable to be buried in the ground under water, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade provided in the front end thereof with a sharp knife edge and attached to said tubular body in the rear of said cultivating blade and having side surfaces gradually diverging towards the rear portion thereof, said vertically mounted plow-type digging blade consisting of a hollow soil repelling element and a digging element swingably mounted in the front of said hollow soil repelling element, said hollow soiL repelling element including a swing mechanism for swinging to and fro said digging element in the moving direction thereof.
 5. A plow-type cable-burying device as claimed in claim 4 wherein said hollow soil repelling element is provided with a weight incorporated therein.
 6. A plow-type cable burying device comprising a tubular body consisting of a cable inlet portion extending in a direction in parallel with the ground under water, an intermediate bent portion gradually bent downward, and a cable outlet portion opened at the bottom of a trench being dug by the device, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade secured to said intermediate bent portion of said tubular body and provided in the front end thereof with a sharp knife edge and having side surfaces gradually diverging towards the rear portion thereof, a plurality of cable guide cylinders each consisting of two cylinder halves each having flanges, and held together by bolts passing through said flanges with said towing wires sandwiched therebetween and arranged side by side in the front of said tubular body to form an extension of said tubular body.
 7. A plow-type cable-burying device comprising a tubular body consisting of a cable inlet portion extending in a direction in parallel with the ground under water, an intermediate bent portion gradually bent downward, and a cable outlet portion opened at the bottom of a trench being dug by the device, sledges attached to said tubular body one on each side of its center line, said sledges being adapted to remain in contact with the ground under water in spite of variations in the ground contour and to stabilize the attitude of said tubular body, a metal fitting secured to the front end of said tubular body and adapted to attach at least one towing wire for dragging said tubular body thereto, at least one vertically mounted cultivating blade attached to said tubular body, and a vertically mounted plow-type digging blade secured to said intermediate bent portion of said tubular body and provided in the front end thereof with a sharp knife edge and having side surfaces gradually diverging towards the rear portion thereof, said vertically mounted plow-type digging blade consisting of a hollow soil repelling element and a digging element swingably mounted in the front of said hollow soil repelling element, said hollow soil repelling element including a swing mechanism for swinging to and fro said digging element in the moving direction thereof.
 8. A plow-type cable-burying device as claimed in claim 7 wherein said hollow soil repelling element is provided with a weight incorporated therein. 